As the broadband Internet service, and the third generation cellular phone have lately come into widespread use to be accompanied by expansion in needs for transmission of data large in capacity in the mobile communications system, such as, for example, downloading of music, it is highly hoped that a high-speed and large-capacity data transmission system employing a broadband wireless access technology, such as WiFi, and WIMAX, and so forth, in addition to the cellular wireless system, can be implemented.
3GPP (3rd Generation Partnership Project), and 3GPP 2 (3rd Generation Partnership Project 2), as the standardization group of the third generation cellular phone, have standardized a public cellular phone network technology for an ALL-IP network called IMS (IP Multimedia Subsystem)/MMD (Multimedia Domain). Further, in order to materialize the high-speed and large-capacity data transmission system, the 3GPP, and 3GPP 2 promote standardization by means of 3G Service FMC (Fixed Mobile Convergence) via a WiFi access. The mobile communications system is capable of turning a mobile communications foundation adapted to the ALL-IP by virtue of the 3G Service FMC via the WiFi access. Accordingly, it is possible to implement reduction in cost, and fusion between fixed network communications, and mobile communications. Furthermore, it is possible for a mobile terminal to select optimum communication means according to a location or a state of the mobile terminal.
Since mobile terminals each employing plural communication systems in execution of communication are connected to the mobile communications system, as described in the foregoing, there are needs for flexible execution of various controls, such as charge control, access control, and so forth, owing to diversity in access form.
Further, power is normally supplied to a mobile terminal from a battery, so that the mobile terminal seems to have difficulty with communication for long hours, however, a mobile terminal employed in a cellular wireless system represented by an EVDO system has an idle mode function for temporarily freeing a wireless link while maintaining connection thereof with the Internet if transmission/receipt of data cannot be implemented for a given time length or radio wave signals are weak, during communication, thereby reducing power consumption by virtue of reduction in power consumption of the mobile terminal.
Nevertheless, a mobile terminal connectable to plural mobile communications networks has plural wireless receivers mounted therein, resulting in an increase in power consumption, so that use of the mobile terminal for many hours will pose a problem. According to a technology disclosed in JP-A No. 2003-169379, it is described that in the case where it becomes necessary for a wireless receiver of a wireless system, in non-communicating status or in a status requiring no communication, to communicate with a mobile terminal upon, for example, arrival of an incoming call using a packet to the mobile terminal, the mobile terminal is connected again to an access network by means of a paging function whereby a paging notice including a request for startup of a specified wireless receiver is transmitted from a base station of another wireless system. In the case of using this technology, however, since connection between an access gateway device and the mobile terminal is cut off, there is the need for establishing again the connection between the mobile terminal, and the access gateway device although it is possible to obtain a significant effect of reduction in the power consumption of the mobile terminal. In the case where a service assuming constant connection is provided, in particular, there remains a problem of deterioration in connectability owing to the needs for connecting the mobile terminal to the access network again.
Now, there will be described hereinafter a problem with the access gateway device installed in the mobile communications system. The access gateway device executes access authentication of a mobile terminal to be connected, packet transmission, and so forth, however, there are times when the connection of the access gateway device with the mobile terminal is not correctly freed owing to a change in wireless network status, or power-off due to sudden battery exhaustion. Accordingly, the access gateway device normally monitors the connection status of the mobile terminal by periodically transmitting and receiving a dead peer detection packet in order to check the connection status of the mobile terminal.
A procedure for dead peer detection in a cellular wireless system is specifically described hereinafter with reference to FIG. 22.
FIG. 22 is a view showing a sequence of steps of the procedure for the dead peer detection in a conventional cellular wireless system.
In the figure, MS (Mobile Station) 15 is a mobile terminal connected to a cellular wireless system. PCF (Packet Control Function) 10 is a base station of the EVDO system. Further, PDSN (Packet Data Serving Node) 7 is an access gateway device of the cellular wireless system.
PDSN 7 manages a session with MS 15 by use of PPP (Point-to-Point Protocol).
First, PDSN 7 transmits a dead peer detection packet to MS 15 by use of PPP (step S1).
Next, if MS 15 is in an active status (P1), MS 15 transmits a response packet against the dead peer detection packet as received in the step S1 to PDSN 7 (step S2). Upon receipt of the response packet, PDSN 7 determines that MS 15 is in an enable status of transmitting and receiving data, thereby maintaining the session with MS 15.
Subsequently, if the status of MS 15 makes transition to an out-of-service mode or an idle mode, PDSN 7 transmits the dead peer detection packet to PCF 10 (step S3). Since a wireless link with MS 15 is in a released status (P2A), PCF 10 transmits a paging notice to MS 15 after receiving the dead peer detection packet to MS 15 from PDSN 7. More specifically, PCF 10 transmits a signal to MS 15, advising MS 15 to the effect that an incoming packet has arrived.
Next, if the status of MS 15 is the out-of-service mode, PCF 10 transmits an out-of-service notice to PDSN 7 (this step is not shown in the figure), whereupon PDSN 7 cuts off the session with MS 15 (F1). On the other hand, if MS 15 is an idle mode status, PCF 10 transmits the paging notice to MS 15 in step S4, thereby causing MS 15 to make transition to the active status (P3). Then, PCF 10 transfers the dead peer detection packet received from PDSN 7 to MS 15 (step S5).
Subsequently, MS 15 transmits a response packet against the dead peer detection packet as received to PDSN 7 (step S6). If PDSN 7 receives the response packet from MS 15, PDSN 7 determines that MS 15 is in the enable status of transmitting and receiving data, thereby maintaining the session with MS 15.
Next, if MS 15 has turned power supply OFF (P4), MS 15 first transmits a power-off notice to PDSN 7 (S7). Upon receipt of the power-off notice from MS 15, PDSN 7 frees the session with the relevant MS 15 (F2). As a result of the session between PDSN 7 and the MS 15 being freed, the wireless link between PCF 10 and the MS 15 will be in the released status (P4A).
As described above, because the cellular wireless system is a system having the paging function whereby the paging notice including the request for startup of a specified mobile terminal is transmitted from a base station of a wireless system, it is possible to activate a mobile terminal when the mobile terminal is in an idle mode status, and dead peer detection control is executed, and PDSN can detect a connection status between the mobile terminal and the wireless link from the notice from PCF. Accordingly, with the EVDO system, it is possible to determine that the mobile terminal is in an inactive status if radio waves cannot be received as in the case of the mobile terminal being in the power-off status, or in the out-of-service status, and to determine that the mobile terminal is in a live status in the case of the mobile terminal being in the active status or in the idle mode status.
Next, a procedure for dead peer detection in a wireless LAN system is described hereinafter.
FIG. 23 is a view showing a sequence of steps of the procedure for dead peer detection in a conventional wireless LAN system.
In the figure, MS 15 is a mobile terminal connected to a wireless LAN system. BBR (Broad Band Router) 11 is a broadband router in the wireless LAN system. Further, PDIF (Packet Data Interworking Function) 8 is an access gateway device in the wireless LAN system.
PDIF 8 manages a session with MS 15 by use of IPsec SA (Security Associate). IPsec SA is generated by use of IKE (Internet Key Exchange) at the time of actuating MS 15. Dead peer detection control in the wireless LAN system is implemented by use of the standard function of IKE.
First, PDIF 8 transmits a dead peer detection packet to MS 15 by use of IKE (step S8).
Next, if MS 15 is in the active status (P5), MS 15 transmits a response packet against the dead peer detection packet as received in the step S8 to PDIF 8 (step S9). Upon receipt of the response packet from MS 15, PDIF 8 determines that MS 15 is live, thereby maintaining the session with MS 15.
Then, if PDIF 8 transmits the dead peer detection packet to BBR 11 (step S10) in the case where MS 15 is in the out-of-service mode (P6), BBR 11 transmits a destination-unknown notice to PDIF 8 (step S11) since a wireless link between BBR 11 and MS 15 is cut off. Upon receipt of the destination-unknown notice from BBR 11, PDIF 8 frees its session with MS 15. Upon freeing of the session between PDIF 8 and MS 15, TPsec connection will be in a freed status (P6B).
Next, if MS 15 has turned power supply OFF (P7), MS 15 transmits a power-off notice to PDIF 8 (step S12) as in the case of the EVDO system. Upon receipt of the power-off notice from MS 15, PDIF 8 frees its session with MS 15 (F4). Upon freeing of the session between PDIF 8 and MS 15, the wireless link between BBR 11 and MS 15 will be in a released status (P7A).
Thus, because the wireless LAN system is a system that does not have the paging function, it is not possible with this system to activate the mobile terminal when the dead peer detection control is executed if the mobile terminal is in the idle mode status. Further, PDIF is unable to detect a connection status of the mobile terminal with the wireless link either. In consequence, it is determined with the wireless LAN system that the mobile terminal is in the live status only when the same is in the active status.